Accurate and rapid collection and distribution of geophysical property data provides information for the exploration and production of petroleum resources. Based on data such as electrical and nuclear properties collected in a wellbore, as well as the propagation of sound through a formation, geophysicists make an analysis for operational decisions. The analysis includes determination of whether a well is likely to produce hydrocarbons, whether to drill additional wells in the vicinity of an existing well, and whether to abandon a well as being unproductive. Measurements of the type described herein are also useful in the fields of carbon dioxide (CO2) sequestration, development of methane hydrate deposits, water reservoir and geothermal monitoring, earthquake monitoring, and monitoring for reservoir delineation, among other applications that are known to persons skilled in the art.
Geophysicists may also use wellbore data to select where to set a casing in a well and to decide on how to perforate a well to stimulate hydrocarbon flow. One method of collecting wellbore geophysical properties is by way of well logging. In well logging, a logging tool (also often referred to as a sonde) is lowered into a wellbore on an electrical cable, the wireline. The logging tool is an electrically powered measurement device that may, for example, collect electrical data, sonic waveforms that are propagated through the surrounding formation, or radioactivity counts. These measurements are usually converted to a digital form and transmitted on the wireline. Systems for transmitting data from the wellbore logging tool to a surface acquisition system over a wireline cable are known as wireline telemetry systems.
Typical wireline telemetry systems operate under extreme conditions, such as high temperature, low signal-to-noise ratio (SNR) at the surface and/or downhole receivers due to high distortion caused by a long cable length, among other extreme conditions that are known to exist in wellbores of the type described herein. In wireline telemetry systems, a downhole telemetry module collects data that are sent from one or more measurement tools connected thereto and transmits the downhole data to a surface acquisition system through a cable. Depending on the tool string combination and the wellbore conditions, several types of noise can be generated, which tend to negatively affect the conveyance of data and the performance of the telemetry system.
Logging and monitoring wellbores has been done for many years to enhance and observe recovery of oil and gas deposits. In the logging of wellbores as mentioned above, one method of making measurements underground includes attaching one or more tools to a wireline connected to the surface acquisition system. The tools are then lowered into a wellbore by the wireline and drawn back to the surface (“logged”) through the wellbore while taking measurements. The wireline is usually an electrical cable with limited data transmission capability. Similarly, permanent monitoring systems are established with permanent sensors that are also generally attached to the electrical cable.
Demand for higher data rates for wireline logging tools and permanent monitoring systems is growing rapidly because of higher resolution sensors, faster logging speeds, and additional tools available for a single wireline string. As a consequence of a need for higher data rates, problems in data transmission arise such as degradation of data quality. Therefore, it would be desirable to transfer data between downhole tools and the surface acquisition system with improved signal-to-noise ratio (SNR) so that the quality of the transferred data is not compromised.